(a) Technical Field
The present invention relates to a method of controlling a driver request torque in a hybrid electric vehicle, which can provide a rapid response to the driver request and control a torque discontinuity.
(b) Background Art
A hybrid electric vehicle (HEV) using a motor drive source as an auxiliary power source as well as an internal combustion engine reduces exhaust gas and improves fuel efficiency. The HEV can be driven in an EV mode, which is directed to a purely electric vehicle mode using motor power only, an HEV mode, which is an auxiliary mode using the rotational force of the motor as an auxiliary power source with the use of the rotational force of the engine as a main power source, and a regenerative braking (RB) mode, in which the energy produced when braking the vehicle or the vehicle is driven by inertia is recovered by the motor and charged in a battery. A creep travel mode after a stop is performed by the EV mode.
For the respective driving modes, the logic for calculating a driver request torque should accurately reflect a driver's intention. For the vehicle to be driven as the driver desires, driver's intention to speed up or down the vehicle or maintain a current speed of the vehicle needs to be accurately reflected in the logic. Accordingly, the accuracy of the driver request torque calculation is essentially required for the logic implementation of the HEV.
The factors to be used in interpreting the driver's intention include depression degrees (depths) detected by an accelerator pedal position sensor (APS) and a brake pedal position sensor (BPS). In general, the depression degree of the APS is increased when the driver intends to accelerate, and the depression degree of the BPS is increased when the driver intends to decelerate.
In addition, to calculate a driver request torque that meets the driver's intention and the vehicle system, a transmission shift or a vehicle speed also may need to be reflected.
Moreover, the driver request torque is calculated so that the vehicle can rapidly respond to the driver's intention to accelerate or decelerate the vehicle or maintaining a current speed of the vehicle.
Here, a conventional method of calculating a driver request torque will be described below.
FIG. 3 is a flowchart illustrating a conventional method of calculating a driver request torque. As shown in FIG. 3, the conventional method of calculating a driver request torque comprises the steps of monitoring a vehicle speed, calculating a maximum torque with respect to the vehicle speed, calculating a minimum torque (for a creep travel) with respect to the vehicle speed, monitoring an APS, and calculating a driver request torque according to the APS.
The control and the calculation of the driver request torque are performed by a hybrid control unit (HCU) which is a main controller of the HEV, and a motor control unit (MCU) for controlling the motor.
The conventional method has a drawback, however, which is described with reference to FIG. 4.
FIG. 4 is a torque diagram illustrating an example of calculating the driver request torque.
First, a maximum torque (engine+motor maximum torque) and a minimum torque (motor torque for a creep travel) with respect to a vehicle speed are calculated and, at the same time, an opening degree of the APS is monitored. The term “opening degree” is defined as a depression degree (depth) of the accelerator pedal detected by an APS and is represented as %.
Next, while the minimum torque is matched to 0% of the APS and the maximum torque is matched to 100% of the APS, a driver request torque is obtained according to the calculated vehicle speed and the opening degree of the APS.
In the conventional method of calculating the driver request torque, when, in case where the APS is 0% during vehicle operation, the accelerator pedal is slightly depressed by the driver who intends to accelerate, it is determined that there is no driver request torque and thus the driver request torque is calculated as zero or a negative value. As a result, the response of the vehicle to the driver request torque may be delayed.
For example, in the event that the vehicle speed is 60 kph and the APS is 50% (assuming that the maximum torque is 200 Nm and the minimum torque is −60 Nm at a vehicle speed of 60 kph), the driver request torque is 70 Nm, which has been calculated by determining that there is a driver request torque. However, in the event that the APS is 23%, the driver request torque is calculated as 0 Nm, and in the event that the APS is 10%, the driver request torque is calculated as −47 Nm, thus failing to provide a response that satisfies the driver request torque.
That is, even though the accelerator pedal is depressed by the driver's intention of acceleration at an APS of 10%, the driver request torque is calculated as a negative value, or even though the accelerator pedal is depressed at an APS of 23%, the driver request torque is calculated as 0 Nm, thus failing to provide a rapid response when the driver intends to re-accelerate after coasting (APS=0%) or decelerating.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.